Several different electronic vehicle theft deterrent devices and methods are available, typically belonging to one of two classes of devices—alarm systems and engine immobilizers. Vehicle alarm systems sense unauthorized entry into the motor vehicle and sound an audible alarm or, in the more advanced systems, activate a global positioning system (GPS) locating system. If, after the vehicle alarm system is armed, a door is opened or a window is broken without the system first being disarmed, the system is activated and responds with an audible alarm. Some vehicle alarm systems also incorporate a proximity sensor that activates the theft deterrent alarm if a person or persons is within some predetermined distance from the motor vehicle. The system will usually emit an audible warning that lets the person or persons know the motor vehicle is equipped with an alarm system, thus deterring a break-in before it can occur. Some advanced alarm systems also have shock sensors that will trigger the alarm system if someone tries to forcibly enter the motor vehicle.
Engine immobilizers utilize a coded method of identifying an authorized vehicle operator from an unauthorized vehicle operator. The most common implementation of an engine immobilizer is a vehicle ignition key which includes electronic coding in addition to the traditional mechanical coding. If, during an attempt to operate a motor vehicle, the received electronic code does not match one of the previously identified “valid” codes, engine operation is inhibited through control of one or a combination of starter, fuel system, and spark systems.
While the available systems are able to provide deterrence to theft, some thieves operate by moving the motor vehicle, usually by towing it, to an isolated location where the installed system or systems can be bypassed and parts can be stripped off the motor vehicle. To combat this, vehicle alarm systems are available today with a motion sensor that triggers the alarm system if the motor vehicle is moved when the system is armed. Motion-based alarm systems typically incorporate “tilt” switches that activate the motor vehicle alarm if the motor vehicle is tilted, such as when it is towed, or otherwise moved. Suspension displacement transducers are often used as well to sense unauthorized vehicle movement. However, these sensors are expensive additions to the motor vehicle and are limited to the effectiveness of the alarm system. Additionally, fraudulent claims of vehicle theft continue to comprise a significant percentage of all vehicle theft claims. Engine immobilizers make the possibility of theft without a valid ignition key extremely remote; however, the possibility remains that a vehicle equipped with an immobilizer could be towed or pushed away.
Accordingly, a need exists for a vehicle theft detection device and method that can provide a motor vehicle motion-sensitive deterrent system that is reliable and that uses inexpensive or preexisting sensors to keep the price of the system low.